Abstract

The Tec family tyrosine kinase, Itk, regulates signaling downstream of the TCR. The absence of Itk in CD4+ T cells results in impaired Th2 responses along with defects in maturation, cytokine production, and survival of iNKT cells. Paradoxically, Itk−/− mice have spontaneously elevated serum IgE levels, resulting from an expansion of the Vγ1.1+Vδ6.3+ subset of γδ T cells, known as γδ NKT cells. Comparisons between γδ NKT cells and αβ iNKT cells showed convergence in the pattern of cell surface marker expression, cytokine profiles, and gene expression, suggesting that these two subsets of NKT cells undergo similar differentiation programs. Hepatic γδ NKT cells have an invariant TCR and are derived predominantly from fetal progenitors that expand in the thymus during the first weeks of life. The adult thymus contains these invariant γδ NKT cells plus a heterogeneous population of Vγ1.1+Vδ6.3+ T cells with diverse CDR3 sequences. This latter population, normally excluded from the liver, escapes the thymus and homes to the liver when Itk is absent. In addition, Itk−/− γδ NKT cells persistently express high levels of Zbtb16 (PLZF) and Il4, genes that are normally downregulated in the most mature subsets of NKT cells. These data indicate that Itk signaling is required to prevent the expansion of γδ NKT cells in the adult thymus, to block their emigration, and to promote terminal NKT cell maturation.

Footnotes

This work was supported by National Institutes of Health Grants AI084987 and AI083505 (to L.J.B.) and CA100382 (to J.K.). The ImmGen Project is supported by National Institutes of Health Grant AI072073. Core resources supported by the Diabetes Endocrinology Research Center (Grant DK32520) were also used.

The sequences presented in this article have been submitted to the National Center for Biotechnology Information Gene Expression Omnibus Web site (http://www.ncbi.nlm.nih.gov/geo) under accession number GSE15907.